Electrophotographic material and process



United States Patent '3,13Q,338 ELEQTRUPHQTQGRAlHitI MATERHAL AND PRGCESS Heinz Schlesinger, Wiesbaden, Germany, assignor, by mesne assignments, to Azopiate Corporation, Murray Hiil, NJ. 7 No Drawing. Filed Mar. 11, 1969, Ser. No. 14,210 Claims priority, appiication Germany Mar. 18, 1959 32 (Ilaims. (Cl. 96-1) Among modern reproduction processes the electrophotographic process, also known as xerography, is becoming of increasing practical importance. This dry reproduction process is becoming of particular interest in certain fields, for example, office duplicating, and it consists of the application to a material, consisting of'a support and a photoconductive insulating layer adherent thereto, of an electrostatic charge which imparts to the insulating layer the property of light-sensitivity. Such light-sensitive material can be used for the production of images by electrophotographic means; it is exposed to light beneath a master, so that the electrostatic charge is leaked away in the parts of the layer struck by light. The invisible electrostatic image thereby produced is made visible (developed) by powdering over with finely divided, colored, synthetic resin and then made permanent (fixed) by the application to the support of heat.

Material known for the preparation of the photoconductive insulating layers required for the aforedescribed process include selenium, sulphur, zinc oxide, and also organic substances, such as anthracene or anthraquinone. Consideration has also been given to a method of preparation of the photoconductive insulating layers whereby the photoconductive substances, in association with binders, are dispersed in solvents and the resultant dispersions are applied to electrically conductive supports,

primarily metal foils, and dried. However, the photoelectrically sensitizable material thus obtained has not yet satisfied the extensive demands made upon modern duplicating material as regards range of use, reliability, simplicity in handling and, not least in importance, 1ightsensitivity and storageability qualities.

Now it has been found that unexpectedly successful photoelectrically sensitizable layers, with a surprising range of practical applications, are produced if, as photoconductive substances 1,2,5,6-tetraazacyclooctatetraenes (2,4,6,8) are used which correspond to the following general formula in which R R R and R are aryl, or substituted aryl radicals, or heterocyclic radicals of aromatic nature.

Exemplary of the compounds which may be employed in accordance with the present invention are:

Formula 1 3,139,33 Patented June 30, 1964 Formula 2 Formula 4 NN cw-Q G -Q Formula 5 m T l K GK r N Formula 6 Formula 7 Formula 10 o H; -6 N-N Formula 12 Formula 13 The l,2,5,6 tetraaza cyclooctatetraenes (2,4,6,8)-

according to the present invention can be prepared by condensing dihydrazones of aromatics or heterocyclic 1,2-diketones With equimolecular quantities of such 1,2- diketones, either by fusing the reactants with each other at temperatures ranging above 100 C. using, if desired, higher pressure, or by heating the reactants with each other in a dissolved state.

For example, 3,4-di-(4-methoxy-phenyl)-7,8-diphenyl- 1,2,5 ,6-tetraaza-cyclooctatetraene-(2,4,6,8), corresponding to Formula 2, is prepared by heating 11.9 g. (=0.05 mole) of benzil-dihydrazone with 13.5 g. (=0.05 mole) of 4,4-dimethoxy-benzil in a sealed tube for 13 hours to a temperature of 160 C. and purifying the crude product thus obtained by recrystallization from benzene. 3,4,7,8- tetra phenyl 1,2,5,6 tetraaza cyclooctatetraene- (2,4,6,8), corresponding to Formula 1, is prepared, e.g., by heating with reflux 11.9 g. =0.05 mole) of benzildihydrazone with 10.5 g. (=0.05 mole) of benzil for 45 hours in 100 ml. of ethyleneglycol monomethylether, the tetraene precipitating upon cooling and being purified by recrystallization from benzene. All the other 1,2,5,6- tetraaza-cyclooctatetraenes-(2,4,6,8) to be used according to thepresent invention can be prepared by analogous methods, if need be with slight changes in the conditions employed during reaction.

The following schedule contains details of a number of compounds given here as examples of compounds corresponding to the above general formula which are to be used in accordance with the present invention. In the schedule:

Column 1 states the number under which the constitutional formula corresponding to the 1,2,5,6-tetraazacyclooctatetraene-(2,4,6,8) is to be found in the formula list above;

Column 2 states the 1,2-diketone reactant;

Column 3 states the 1,2-diketone-dihydrazone reactant;

Column 5 states the color of the respective 1,2,5,6-tetraaza-cyclooctatetraene- (2,4,6,8)

Degrees 1 Benzil Benzil-dihydrazone. 285-286 C(1)1OI- ess. 2 4,4-dlmethoxy d0 228-229 Do.

benzil. 3 4,4-diethoxydo 187-188 Do.

benzil. 4 4,4-diphenoxyd0 233-234 D0.

benzil. 5 2,2-pyridil d0 270-271 D0. 0 4,4-dimethoxy 4,4'-dimethoxy- 822-323 Do.

. benzil. benzil-dihydrazone. 7 4,4-dipl1en0Xydo 235-236 Do.

benzil. 8 4,4-diethoxybenzil -do 228-229 Do. 9 bis-3,4-methylene- Benzil-dihydrazone.. 249-250 Do.

dihydroxy-benzil (:piperil). 10 4,4-dichl0rbenzil 238 Do. 11 4-dirnethylamin0- 251-252 D0.

. benzil. 12 4-methoxy-benzil 229-230 D0. 13 2,2-dihydr0Xy-5,5- 279-280 D0.

dibrorno-benzil.

The compounds to be used in accordance with the invention have very good light-sensitivity and are particularly suitable for the production of homogeneous layers with unlimited shelf life.

For the preparation of the photoconductive insulating layers, it is advantageous to use solutions or suspensions of the 1,2,5,6-tetraaza-cyclooctatetraenes-(2,4,6,8) of the present invention. As solvents, there may be used organic solvents such as chloroform, benzene, acetone, methylene chloride, ethyleneglycol monomethylether, and others, or mixtures of such solvents. The compounds to be used according to the present invention can also be used in admixture with each other or with other organic photoconductive substances.

As has further been discovered, 'it may be an advantage in the production of the photoconductive layers for organic Water-insoluble resins to be used in association With the compounds in accordance with the invention and corresponding to the general formula given above. The following may appropriately be mentioned: water-insoluble natural and synthetic resins, e.g., balsam resins, phenol resins modified with colophony, and other resins of which colophony constitutes the major part, coumarone resins and indene resins and the substances covered by the collective term synthetic lacquer resins, which according to the Kunststofiftaschenbuch (Plastics Pocket Book) published by Saechtling-Zebrowski (11th edition, 1955, page 212 at seq.) include processed natural substances such as cellulose ether; polymers such as polyvinyl chlorides, polyvinyl acetate, polyvinyl acetals, polyvinyl ethers, polyacrylic and polymethacrylic esters, as also polystyrene and isobutylene; polycondensates, e.g., polyesters, such as phthalate resins, alkyd resins, maleic acid resins, maleic acid/ colophony/ mixed esters of higher alcohols, phenolformaldehyde resins, particularly colophony-modified phenol formaldehyde condensates, ureaformaldehyde resins, melamine-formaldehyde condensates, aldehyde resins, ketone resins of which particular mention is to be made of AW 2 resins of the Badische Anilinund Sodafabrik, xylene formaldehyde resins and polyamides; and polyadduc'ts, such as polyurethanes. f

If the tetraaza-cyclooctatetraene compounds to be used in accordance with the invention are used in association with organic Water-insoluble resins, the proportion of resin to photoconductive substance can vary very greatly. The use of mixtures of approximately equal parts of resin and l,2,5,6-tetraaza-cyclooctatetraene-(2,4,6,8) compound has been found advantageous. If such mixtures of approximately equal parts of resin and tetraene compound are used, their solution in most cases gives, on drying, transparent layers which are regarded as solid solutions.

The base materials used as electroconductive supports may be any that satisfy the requirements of xerography,

e.g., metal or glassplates, paper or plates or films made of resins or plastics. If paper is to be used as the support for the photoconductive layer, pretreatment of the paper against penetration of the coating solution is advisable, e.g., with methyl cellulose in aqueous solution or polyvinyl alcohol in aqueous solution or with a solution 111 acetone and methylethylketone of a copolymer of acrylic acid methyl ester and acrylonitrile or with solutions of polyamides in aqueous alcohols. Aqueous dispersions of substances suitable for thepretreatment of the paper surface may also be used. a

The solutions of the compounds to be used in accordance with the invention, with or without the resins, are applied .to the supports in the usual manner, for example by spraying, by direct application, by means of rollers and the like, and are then dried in order to produce a homogeneous photoconductive layer on the electroconductive support. a

After the layers have beenpositively or negatively charged, by means of, for example, a corona discharge, they are light-sensitive and canbe used advantageously with long-Wave UV. light of 36004200 A. for electrophotographic image production. Very short exposure under a master to a high pressure mercury lamp will give good images. a

The further discovery has been made that the light sensitivity to the visible range of the spectrum of the photoconductive layer can be highly improved by means of sensitizers. As sensitizers, dyestuifs inparticular are suitable, for the readier identification of which the number is given under which they are listed in Schultz Farbstofftabellen (7th edition, 1st vol., 1931). The following are examples of particularly effective sensitizers: triarylmethane dyestuffs such as Brillant Green (No. 760, p. 31 4), Victoria Blue B (No. 822, p. 347), Methyl Violet (No. 783, p. 327), Crystal Violet (No. 785, p. 329), Acid Violet 6B (N0. 831, p. 351), xanthene dyestutfs, namely rhodamines, such as Rhodamine B (No. 864, p. 365), Rhodamine 66 (No. 866, p. 366), Rhodamine G Extra (No. 865, p. 366), Sulphorhodamine B (No. 863, p. 364) and Fast Acid Eosin G (No. 870, p. 368), as also phthaleins such as Eosin S (No. 883, p. 375), Eosin A (No. 881, p. 374), Erythrosin (No. 886, p. 376), Phloxin (No. 890, p. 378), Bengal Rose (No. 889, p. 378), and Fluorescein (No. 880, p. 373), thiazine dyestuffs such as Methylene Blue (No. 1038, p. 449), acridine dyestuffs such as Acridine Yellow (No. 901, p. 383), Acridine Orange (No. 908, p. 387) and Trypaflavine (No. 906, p. 386), quinoline dyestuifs such as Pinacyanol (No. 924, p. 396) and Cryptocyanine (No. 927, p. 397), quinone dyestuffs and ketone dyestuifs such as Alizarin (No. 1141, p. 499), Alizarin Red S (No. 1145, p. 502) and Quinizarine (No. 1148, p. 504), cyanine dyestulfs, e.g. Cyanine (No. 921, p. 394) and chlorophyll. The production of images by electrophotographic means is performed as follows: when the photoconductive layer has been charged by means of, for example, a corona discharge with a charging apparatus maintained at 6000- 7000 volts, the support, e.g., paper or aluminum foil or plastic film, with the sensitized coating, is exposed to light under a master or by episcopic or diascopic projection and is then dusted over in known manner With a resin powder colored with carbon black. The image that now becomes visible can be easily wiped oif. It therefore must be fixed; it can, for example, be briefly heated to about 120 C. or, according to the fusion temperature of the developer used, it can be exposed to infrared radiation. The temperature required is less if the heat treatment is effected in the presence of vapors of solvents such as trichloroethylene, carbon tetrachloride or ethyl alcohol. The fixing of the powder image can also be accomplished by steam treatment. From positive masters, positive images, characterized by good contrast, are produced.

If transparent supports are used, the electro-photographic images can also be used as masters for the production of additional copies on any type of light-sensitive sheet. In this respect the photoconductive compounds to be used as provided by the invention are superiorto the substances used hitherto, such as selenium or zinc oxide, inasmuch-as the latter produce only cloudy layers not readily capable of further reproduction, because solid solutions can not be produced with these materials, and only suspensions are possible.

If translucent supports are used for photoconductive layers such as are provided by the invention, images'can also be produced by the reflex process. The production of a reflex copy also constitutes an advance over the known art. Moreover the photoconductive layers prepared in accordance with the invention have a further important advantage in that they can be charged positively as well as negatively. With positive charging the images are particularly good and evolution of ozone, which with negative charging is very copious and, because it is injurious to health calls for the adoption of special measures, such as the installation-of fans, is scarcely to be detected.

The invention will be furtherillustrated by reference to the following specific examples:

Example 1 0.5 g. of 3,4-di-(4rphenoxy-phenyl)-7,8-diphenyl-1,2, 5,6-tetraaza-cyclooctatetraene-(2,4,6,8) corresponding to Formula 4, and 0.5 g. of a ketone resin, e.g., the product commercially'available under the designation Kunstharz EM, are dissolved in 15 ml. of chloroform and the solution is coated onto paper, the surface of which had been pretreated to, prevent the penetration of organic solvents, and dried. By means of the thus coated paper, a direct image is produced in an electrophotographic process. With a corona discharge produced by means of a charging apparatus maintained at about 6000 volts, the coated dried layer is provided with a negative electric charge, then exposed under a positive original using a high pressure mercury lamp, and then dusted over in known manner with a developer powder.

The developer used consists of small glass balls and a very finely divided resin-carbon black mixture. The black colored resin adheres to those parts of the layer which were not struck by light during exposure and, thus, a positive image of the original becomes visible, which is fixed by heating.

The developer used consists of g. of glass balls of .a particle size from 300 to 400 and 2.5 g. of a toner having a particle size from 20 to 50 The toner is produced by meltlng together, grinding and sitting:

30 g. polystyrene,

30 g. of resin-modified maleic acid resin, e.g., the prod uct commercially available under the registered trademark Beckacite K105, and L 3 g. of carbon black, e.g., the product commercially available under the designation Peerless Black Russ 552.

Example 2 Paper is coated as described in Example 1 and the layer thus produced is positively charged by means of a corona discharge. After exposure under an original, the

7 Example 3 In 15 mL-of chloroform there is dissolved a mixture consisting of:

0.2 g. 3,4,7 ,8-tetraphenyl-1,2,5 ,6-tetraazacyclooctatetraene- (2,4,6,8) corresponding to Formula 1,

0.2 g. 3,4 di (4'-phenoxy-phenyl)-7,8-di-(4"-methoxyphenyl) 1,2,5,6 tetraaza-cyclooctatetraene-(2,4,6,8) corresponding to Formula 7, and

0.2 g. 3,4 di (4-ethoxy-phenyl)7,8-diphenyl l,2,5,6-

tetraaza-cyclooctatetraene-(2,4,6,8) corresponding to Formula 3.

The solution thus obtained is coated onto an aluminum foil and dried to form a layer which adheres firmly to the support. An electrophotographic image is produced on this material in known manner.

Example 4 Example 5 The process described in Example 1 is followed with the modification that for coating the base paper a solution is used containing 0.5 g. of 3,4-di-(4'-methoxy-phenyl)- 7,8 diphenyl-l,2,5,6-tetraaza-cyclooctatetraene-(2,4,6,8) corresponding to Formula 2, and 0.5 g. of Zinc resin, e.g., of the product commercially available under the designation Erkazit Zinkharz 165, in 15 ml. of chloroform.

Example 6 0.5 g. of 3,4-di-pyridyl-(2')-7,8-diphenyl-1,2,5,6-tetraaza-cyclooctatetraene-(2,4,6,8 corresponding to Formula 5, and 0.5 g. of a ketone-aldehyde condensation resin, e.g., the product commercially available under the designation Kunstharz AP are dissolved in 3 ml. of chloroform and the solution is coated onto a superficially roughened aluminum surface. After evaporation of the solvent, a layer remains'which adheres firmly to the surface of the aluminum foil. The thus coated foil is treated as described in Example 1 whereby after fixing the powder image, a positive image is produced on the aluminum surface.

Example 7 0.5 g. of 3,4,7,8-tetraphenyl-1,2,5,6-tetraaza-cyclooctatetraene-(2,4,6,8), corresponding to Formula 1, and 0.5 g. of polyvinylacetate, e.g., the product commercially available under the registered trademark Mowilith 50, and 0.5 mg. of Rhodamine B-extra (Schultz, Farbstoiftabellen, 7th edition, vol. 1, No. 864), dissolved in 0 .1 ml. of methanol, are dissolved in 7 ml. of chloroform and an aluminum foil is coated with this solution. After drying, an electrophotographic image is produced as described in Example 1, but instead of a high pressure mercury lamp, a 100 watt incandescent lamp is used for exposure.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. An electrophotographic material comprising ductive support layer and a photoconductive insulating mula layer, the latter" comprising a compound having the formula in which R R R and R are selected from the group consisting of aryl groups and heterocyclic groups of aromatic nature.

2. An electrophotographic material according to claim 1 in which the photoconductive layer contains an organic water-insoluble resin. 7

3. An electrophotographic material according to claim 1 in which the photoconductive layer contains an optical sensitizer. V

4. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula 5. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the for- 6. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula 7. An electrophotographic material comprising a conductive support layer and a photoconductive insulating N N C a l Q layer, the latter comprising a compound having the formula r 8. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula 9. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the for 10. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula 11. An electrophotographic material comprising a conductive support layer 'and a photoconductive insulating layer, the latter comprising a compound having the formula CHaO- CHzO- 12. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula ffCgLiHi 13. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula 14. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula 15. An electrophotographic material comprising a conductive support layer and a photoconductive insulating in layer, the latter comprising a compound having the formula 16. A photographic reproduction process which comprises electrically charging a supported photoconductive insulating layer, exposing it to light under a master, and developing the resulting image, the photoconductive layer comprising a compound having the formula 20. A photographic reproduction process which c0m prises electrically charging a supported photoconductive insulating layer, exposing it to light under a master, and

developing the resulting image, the photoconductive layer comprising a compound having the formula Q 21. A photographic reproduction process which comprises electrically charging a supported photoconductive insulating layer, exposing it to light under a master, and developing the resulting image, the photoconductive layer comprising a compound having the formula N- '22. A photographic reproduction process which comprises electrically charging a supported photoconductive insulating layer, exposing it to light under a master, and

developing the resulting image, the photoconductive layer comprising a compound having the formula 23. A photographic reproduction process which com- 29. A photographic reproduction process which comprises electrically charging a supported photoconductive prises electrically charging a supported photoconductive insulaung layer, exposing it-to light under a master, and insulating layer, exposing it to light under a master, and develop ng the resulting image, the photoconductive layer developing the resulting image, the photoconductive layer compnsing a compound having the formula 5 comprising a compound having the formula N N l /N-N\ OH: Q Q N i l CH;

' N-N Q 30. A photograph1c reproduction process which co n 24 A Photographic reproduction process which prises electrically charging a supported photoconductive prises electrically charging a supported photoconductive msulatlqg layer 6x13951115 It to hght under and insulating layer exposing it to light under a master, and develop ng the resulting image, the photoconductive layer developing the resulting image, the photoconductive layer compnsmg a compound havmg the formula comprising a compound having the formula 25. A photographic reproduction process whichcomprises electrically charging a supported photoconductive An electrophomgraphlc matenal comPnslPg f insulating layer, exposing it to light under a master, and 0 ducnve Support layer a photoconductlve mulalmg developing the resulting image, the photoconductive layer layer the latter compnsmg a Compound havmg the comprising a compound having the formula formula N OH can a A :3, 3 i 3 3 26. A photographic reproduction process which com- 4O \O prises electrically charging a supported photoconductive insulating layer, exposing it to light under a master, and developing the resulting image, the photoconductive layer comprising a compound having the formula I r 32. A photographic reproduction PI'OCGSS'WhlCh comprises electrically charging a supported photoconductive I-I:OC C -'OC2H5 insulating layer, exposing it to light under a master, and l I developing the resulting image, the photoconductive layer 02m comprising a compound having the formula N-N OH 27. A photographic reproduction process which comprises electrically charging a supported photoconductive 1 C insulating layer, exposing it to light under a master, and 7 developing the resulting image, the photoconductive layer O C comprising a compound having the formula i B 3 I l References Cited in the file of this patent f UNITED STATES PATENTS 28. A photographic reproduction process which com- 2,663,636 Middleton Dec. 22,5195? prises electrically charging a supported photoconductive 2,859,211 Pfister et a1. Nov. 4, 1958 insulating layer, exposing it to light under a mas er, and 2,878,245 Moore et al. I Mar. 17, 1959 developing the resulting image, the photoconductive layer 2,937,944 Van Dorn et a1 May 24, 1960 comprising a compound having the fommla 2,940,848 Kostelec et al. June 14, 1960 (April 1954). TS1080. P29.

Baines: The Science of Photography, Fountain Press (1958), pages 104-105.,TR200. B3.

0 OTHER REFERENCES 7 Siegrist: Das Papier, vol. 8, No. 7/8, pages 109-120 

1. AN ELECTROPHOTOGRAPHIC MATERIAL COMPRISING A CONDUCTIVE SUPPORT LAYER AND A PHOTOCONDUCTIVE INSULATING LAYER, THE LATTER COMPRISING A COMPOUND HAVING THE FORMULA 